the present invention relates to rotary fluid pressure devices, and more particularly, to such devices of the type which typically include a gerotor gear set, and a stationary valve member disposed adjacent the gerotor gear set.
Rotary fluid pressure devices which include a gerotor gear set as the fluid displacement mechanism are typically used as low-speed, high-torque motors. Such gerotor motors have traditionally been classified as being either of the "spool valve" type, or of the "disc valve" type. In a spool valve gerotor motor, the valving is accomplished at a cylindrical interface between a spool valve and a surrounding housing. In a disc valve type, the valving is accomplished at a flat, transverse planar interface of a disc valve and a stationary valve member.
More recently, a particular type of disc valve motor has been developed which is sometimes referred to as a "valve-in-star" motor. In this type of motor, a disc valve element is recessed within one axial end face of the gerotor star, and the valving action occurs between the axial end surface of the star and disc valve and the adjacent surface of a stationary valve member. Such valve-in-star motors are illustrated and described in U.S. Pat. Nos. 4,715,798; 4,741,681; 4,756,676; and 4,976,594, all of which are assigned to the assignee of the present invention and incorporated herein by reference.
It should be understood by those skilled in the art that, although the present invention is not limited to use in rotary fluid pressure devices of the valve-in-star type, the invention is especially suited for use in conjunction with such devices, and will be described in connection therewith.
Many gerotor motors of the type sold commercially by the assignee of the present invention include some sort of shuttle valve. In some motors, the only purpose for the shuttle valve is to communicate a relatively small flow of fluid from the low pressure side (downstream of the gerotor) of the motor to a case drain port, from where the fluid flows through a heat exchanger, to prevent overheating of the system fluid. Such shuttle valves are typically located in the endcap casting which defines the inlet and outlet ports of the motor. A typical shuttle valve of the type and for the purpose described above, and which is in commercial usage by the assignee of the present invention is illustrated and described in U.S. Pat. No. 4,343,601, assigned to the assignee of the present invention and incorporated herein by reference.
In some gerotor motors, a shuttle valve arrangement is included to divert a relatively small lubricant flow from the main flow path, and direct the lubricant flow through various parts of the motor which need lubrication, such as spline connections and bearings. An example of a gerotor motor including a shuttle valve used to divert lubricant flow is illustrated and described in U.S. Pat. No. 4,645,438, assigned to the assignee of the present invention and incorporated herein by reference.
Finally, in gerotor motors of the valve-in-star type, in which there is a stationary valve plate disposed adjacent the gerotor, the side of the stationary valve plate axially opposite the gerotor typically defines a pressure balancing region, as is illustrated and described in above-incorporated U.S. Pat. No. 4,976,594. In such motors, assuming bi-directional operation is desired, it is necessary to provide some means to communicate system pressure (the pressure at the inlet port of a motor) to the pressure balancing region, in order to bias the stationary valve member into sealing engagement with the adjacent surface of the gerotor and valve-in-star. This is done to reduce leakage along the face of the gerotor and improve volumetric efficiency of the motor.
In motors of the type shown in above-incorporated U.S. Pat. No. 4,976,594, the shuttle valve has been disposed in the endcap casting, and has typically included the assembly of spools, poppet members, sleeves, springs, and plug members illustrated and described in above-incorporated U.S. Pat. No. 4,343,601. Although such shuttle valve arrangements have generally performed satisfactorily for the intended purpose, the substantial number of parts in the shuttle assembly, and the extra machining required in the endcap casting has added substantially to the size, complexity, and expense of the entire endcap assembly, thus increasing the overall size, weight, and expense of the entire motor.
In addition, the use in valve-in-star motors of the type of shuttle arrangement illustrated and described in above-incorporated U.S. Pat. No. 4,343,601 has been used only to provide low pressure fluid to the lubrication circuit, and from there the fluid flows to a case drain, and then to the system cooler. Communicating high pressure fluid to the pressure balancing region has required additional structure.